Ferro-alloy process and product

ABSTRACT

This invention is directed to the making of a ferro-nitrogen addition agent for steel making processes. The ferro-nitrogen agent is derived in my process from waste materials of steel making and processing.

This is a continuation-in-part of the application for a patent, whichwas filed on May 5, 1977 under the Ser. No. 794,106 Group 223 and whichis abandoned.

BACKGROUND OF THE INVENTION

It is known that, in the fabrication of several types of steel theincorporation of the nitrogen(N) leads to the formation of stablenitrides with elements such as chromium(Cr), vanadium(V), niobium(Nb),aluminium(Al), etc., improving the austenitic structure of steel.

It is also known that, in certain cases, the nitrogen can replace, insome proportion, the nickel(Ni), due to its powerful gammageneproperties.

In the iron crystal-structure, the nitrogen takes an interstitialposition, which creates a distortion of the structure and contributes tothe decrease in the size of the crystal-structure and the increase inthe resistance to grain growth in working.

The nitrogen bearing steels, especially the stainless steels withchromium, are more ductile, more workable over a wider range of chromiumcontent. Cold forming operations may be carried out more succesfullyover a wider range of temperatures.

Further, the tensile strength of commercial steels is much improved bythe presence of nitrogen. A small proportion of nitrogen (i.e. 0.008%)can improve the yield point and thus replace a certain quantity ofmanganese(Mn), which disturbs the rimming process in the big moulds(over 15 tons ingots). This is the reason for the tendency to alloy therimmed steel with nitrogen.

Regarding the art of introducing nitrogen into the liquid steel, thefollowing methods should be mentioned:

The introduction of molecular nitrogen in liquid steel through nozzlesor perforated electrodes, below the slag layer and its conversion intoatomic state, which is incorporated by the liquid steel,

The blowing of compressed air or nitrogen-gas through the lance of theconverter, together with oxygen, or the blowing of molecular nitrogen orammonia(NH3) in the ladle through porous refractories,

The introduction of organic substances containing nitrogen into theliquid steel (in furnace or ladle),

The introduction of nitrogen bearing refined ferro-alloys(ferro-manganese or ferro-chromium) into the liquid steel (in furnace orladle).

With the exception of the ferro-alloy method, all the other methods havea limited field of application or a nitrogen assimilation with a highdegree of dispersion.

The ferro-alloy method is used more often because it facilitates thenitrogen penetration into the liquid steel in a wide range of nitrogencontent and with a small scattering of the assimilated nitrogen.

However, due to the manganese or chromium content in the final analysisof the steel, there is a limit to the amount of nitrogen which can beintroduced, because together with the nitrogen important quantities ofmanganese or chromium are assimilated into the steel (10-15 times morethan nitrogen). These refined ferro-alloys bear high contents ofmanganese or chromium and therefore are more expensive than the standardferro-alloys.

This invention discloses a new type of ferro-alloy, the FERRO-NITROGENor NITRIDED IRON, which bears an important content of nitrogen but isfree of other elements such as manganese or chromium.

The FERRO-NITROGEN keeps the advantages of the conventional ferro-alloysmethod but is not limited in its usage by the presence of manganese orchromium. The FERRO-NITROGEN can be used in the fabrication of any typeof steel in which the presence of nitrogen is necessary for theachievement of all the improvements the nitrogen conveys to the physicalproperties of the steel.

SUMMARY OF THE INVENTION

This invention relates to FERRO-NITROGEN and the art of producing it.

One object of our invention is the provision of a process for producinga ferro-alloy containing as prime element the nitrogen, without thepresence of other elements such as manganese or chromium, usuallyexistent in the known ferro-manganese or ferro-chromium, which bearnitrogen and are used in the fabrication of various types of steel,including stainless steels.

The use of FERRO-NITROGEN will prevent the introduction of certainquantities of manganese or chromium in the fabrication of several typesof steel, in which these elements are undesirable.

Another object of our invention is to use inexpensive raw materials,such as:

metallic ejections (grits, sludges, powder from exhausted fumes-fluedust) resulting from various steel making processes,

iron oxides (powder and scale), steel powder and iron powder resultingfrom secondary steel processes such as forging, rolling, drawing, etc.,

iron pellets and their residual powder,

iron powder.

The FERRO-NITROGEN will be produced by treating accordingly thementioned raw materials, under the following conditions:

grinding the raw materials and separating (size selection) the finepowder with particles smaller than 30 microns,

reducing the fine powder of iron oxides with hydrogen or carbon monoxideat a temperature of 1400°-1600° F. (760°-870° C.). To avoid the stickingof the iron powder an addition of fine silica(SiO2) should be used. Thefinal grading of the iron powder must be below 30 microns.

diffusing atomic nitrogen into the iron or steel powder in order toobtain iron nitride with a content of nitrogen up to 6%. For thisoperation should be used a rotary furnace or a fluidized bedinstallation at a temperature of 1100°-1350° F. (590°-730° C.). Bypassing through the installation, loaded with iron powder, anhydrousammonia(NH3) with at least 98% concentration and a pressure of up to 8inches (200mm) water column, the ammonia will be dissociated in hydrogenand atomic nitrogen, which at the mentioned temperature (1100°-1350° F.(590°-730° C.) will diffuse into the iron powder, forming ironnitride(mostly Fe4N).

The duration of this nitriding process depends on the grading of theiron particles (about 5 min. for 1 micron, 8.5 hours for 10 microns andmore than 48 hours for 20 microns. A prior grading of the iron powderwill indicate the nitriding time.

Before and after the nitriding process, the installation should bewashed by passing-through argon or molecular nitrogen.

briquetting the nitrided iron powder with a mineral binder such ascalcium monoxide(CaO), etc..

packing.

The FERRO-NITROGEN will be used as ferro-alloy in the steel makingprocess and when in contact with liquid steel, the iron nitride Fe4N,which is instable over about 930° F. (500° C.), is dissociated in ironand atomic nitrogen, which are assimilated into the liquid steel with anefficiency of 90-95%. During the solidification period of the steel thenitrogen atoms are taking, in the iron crystal-structure, aninterstitial position, which creates the distortion of the structure,securing a high degree of the structural uniformity of the steel.

The FERRO-NITROGEN can be added either during the melting process, inthe furnace, or in the ladle, before or during the tapping operation ofthe liquid steel.

The FERRO-NITROGEN is not toxic and its handling does not create toxicalwork conditions; in liquid steel this ferro-alloy does not eliberatetoxic gases and therefore no special measures of precaution arenecessary.

Using the above mentioned raw materials, the fabrication of theFERRO-NITROGEN will thus not depend on expensive or strategicalmaterials, difficult to obtain. Some of the above mentioned materialsare waste, normally trown-away by the steel producers, their recyclingbeing an expensive operation. Another object of our invention is toproduce iron powder by treating accordingly (separation, size selection,reduction, etc.) the iron oxides (powder and scale), the steel powderand iron powder resulting from exhausted fumes, flue dust, of varioussteel making processes and from secondary steel processes such asrolling, forging, drawing, etc..

Another object of our invention is the provision of a method ofintroducing nitrogen into steel by adding to the liquid steel, in thefurnace or ladle, the FERRO-NITROGEN as produced by the methodpreviously described.

Inasmuch as many embodiments are possible of our invention and manymodifications may be made of the indicated embodiments, we desire thatall matter described herein be considered by way of illustration and notby of limitation.

The embodiments of this invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A method of producing aferronitride comprising mixing flue-dust containing iron oxide withmetallic iron ejections consisting of grits, sludges or powders to forma mixture which contains no alloyed manganese or chromium, grinding saidmixture to form a fine powder, grading said fine powder to obtain afraction of below 30 microns in size, reducing the iron oxide in saidfraction to metallic iron thereby forming a metallic fraction, nitridingsaid metallic fraction to form a ferro-nitride.
 2. The method of claim1, wherein said fraction is reduced at a temperature in the range of1400°-1600° F.
 3. The method of claim 1, wherein said fraction isreduced with hydrogen.
 4. The method of claim 1, wherein said fractionis reduced with carbon monoxide.
 5. The method of claim 2, whereinmetallic iron is nitrided with atomic nitrogen.
 6. The method of claim2, wherein metallic iron is nitrided at a temperature in the range of1100°-1350° F.
 7. The method of claim 5, wherein the atomic nitrogen isderived from the dissociation of ammonia.
 8. The method of claim 7,wherein the ammonia is introduced at a pressure of up to 8 inches watercolumn.
 9. The method of claim 1, wherein said fraction selected is lessthan 20 microns and is nitrided for a time up to 48 hours.
 10. Themethod of claim 1, wherein said fraction selected is less than 5 micronsand is nitrided for a time up to 6 hours.
 11. The method of claim 1,wherein said fraction selected is less than 1 micron and is nitrided fora time up to 10 minutes.
 12. The method of claim 1, wherein saidferronitride is briquetted.
 13. The method of claim 12, wherein the saidferronitride powder is briquetted with a mineral binder.
 14. The methodof claim 1, further comprising adding said ferronitride to a furnace orladle of liquid steel.